(1) Field of the Invention
The present invention relates to a laminated non-woven fabric having excellent softness and strength and to a process for producing the same. More specifically, the invention relates to a laminated non-woven fabric comprising an intermediate layer of a melt-blown non-woven fabric composed of an olefin-type resin, and inner and outer layers of a spun-bonded non-woven fabric consisting of a polyester-type fiber, which are laminated one upon another, the intermediate layer and the inner and outer layers being bonded together owing to the intermingled fibers, and further relates to a process for producing the same.
(2) Description of the Related Art
A melt-blown non-woven fabric is obtained by extruding a molten resin into fine resin streams which are then brought into contact with a heated gas of a high speed thereby to form non-continuous fibers of fine diameters, and then integrating the fibers on a porous support material. The melt-blown non-woven fabric is relatively soft and is, hence, used for such applications as clothing and medical supplies.
In these applications, however, the melt-blown non-woven fabric by itself lacks strength and exhibits its particular slimy feeling. Therefore, means has been employed to reinforce the melt-blown non-woven fabric and to improve its touch by sticking to it another non-woven fabric obtained by the spun-bonding method or by any other method.
Several kinds of laminated non-woven fabrics have already been proposed in which a non-woven fabric such as a melt-blown non-woven fabric is laminated on a spun-bonded non-woven fabric. For instance, Japanese Patent Publication No. 11148/1985 discloses a non-woven fabric material comprising a web of substantially continuous filaments which have an average filament diameter of greater than about 12 microns and which are deposited in a random fashion and are molecularly oriented, and an integrated mat of largely non-continuous thermoplastic polymeric micro fibers having an average fiber diameter of smaller than about 10 microns and a softening point which is lower by about 10.degree. C. to 40.degree. C. than the softening point of the continuous filaments, the web and the mat being arranged to establish a laminar relationship and bonded together to form intermittently and discretely bonded regions upon the application of heat and pressure.
Moreover, Japanese Patent Publication No. 51725/1988 discloses a laminated non-woven fabric used for a filtering cloth of an air cleaner, wherein a sheet-like spun-bonded fiber layer consisting of thermoplastic synthetic long fibers in which fibers are partly bonded together due to the thermal melt-adhesion, is arranged on one side of an intermediate fiber layer consisting of polyester staple fibers having a thickness of 1 to 6 deniers and a fiber amount of 40 to 60 g/m.sup.2, a fiber layer consisting of a mixture of two kinds of polyester staple fibers having different thicknesses is arranged on the other side of the intermediate fiber layer, these fiber layers are coupled together as a unitary structure by partly intermingling the fibers of these fiber layers relying upon the needle-punching or the like working, and a resin adhesive is adhered onto the fiber layers which are coupled together as a unitary structure.
Japanese Patent Publication No. 2060/1987 discloses a laminated non-woven sheet for micro filters, which comprises a spun-bonded non-woven fabric consisting of drawn fibers and a sheet (melt-blown non-woven fabric sheet) in which undrawn fibers having an average fiber diameter of smaller than 0.8 denier are melt-adhered to one another, and wherein the undrawn fiber sheet is laminated and bonded under the non-solidified condition onto the spun-bonded non-woven fabric.
Furthermore, Japanese Laid-Open Utility Model Publication No. 102615/1981 discloses a laminated non-woven fabric filter comprising an upper layer of a web constituted by staple fibers of 1 to 20 deniers, an intermediate layer of a web constituted by staple fibers of a denier smaller than that of the upper layer, and a lower layer consisting of a long fiber non-woven fabric having an apparent density of from 0.1 to 0.5 g/cm.sup.3, which are coupled together by the needle-punching.
The laminated non-woven fabric in which the melt-blown non-woven fabric and the spun-bonded non-woven fabric are laminated one upon the other, has a suitable degree of permeability and water resisting property, and is suited for such applications as clothing. However, the laminated non-woven fabric of this kind has heretofore been obtained by sticking and laminating the melt-blown non-woven fabric and the spun-bonded non-woven fabric together by applying the heat and pressure like the heat-embossing, or by laminating the two non-woven fabric layers by locally intermingling the fibers thereof by the needle-punching or the water-punching, or by sticking and laminating them together by the ultrasonic-wave working. When they are melt-adhered by the heat, therefore, the melt-adhered portions are solidified and stiffened to impair softness, touch and hand. When they are joined together by the needlepunching or water-punching, the non-woven fabric layer becomes locally uneven and is deviated. Moreover, filaments are broken at the punched portions, deteriorating the junction strength between the non-woven fabric layers.
Even when the non-woven fabrics are stuck together by the ultrasonic-wave working, there develop inconveniences nearly similar to those of when they are melt-adhered together by the heat-embossing.
Thus, there have not yet been provided the laminated non-woven fabrics that exhibit in combination softness, porosity and water resisting property possessed by the melt-blown non-woven fabric, and strength, hand, touch and the like properties possessed by the spun-bonded non-woven fabric.
The object of the present invention therefore is to provide a laminated non-woven fabric having excellent softness and strength, in which the melt-blown non-woven fabric and the spun-bonded non-woven fabric are fastened and stuck together free of the above-mentioned defects, and which exhibits softness, porosity, water resisting property and like properties possessed by the melt-blown non-woven fabric and strength, hand, touch and like properties possessed by the spun-bonded non-woven fabric to their maximum degrees, as well as to provide a process for producing the laminated non-woven fabric.
According to the present invention, there is provided a laminated non-woven fabric of a laminated material which comprises an intermediate layer of a melt-blown non-woven fabric obtained by melt-blowing an olefin-type resin, and inner and outer layers of a spun-bonded non-woven fabric which chiefly consists of polyester-type fibers and in which the fibers are bonded together locally and at a coarse density, wherein the fibers constituting the inner and outer layers are inserted in the melt-blown non-woven fabric and are intermingled with fibers in the melt-blown non-woven fabric or in the spun-bonded non-woven fabrics of the opposite sides, so that the layers are coupled together as a unitary structure.
According to the present invention, furthermore, there is provided a process for producing a laminated non-woven fabric having excellent softness and strength, comprising laminating a melt-blown non-woven fabric obtained by melt-blowing an olefin-type resin and spun-bonded non-woven fabrics which consist chiefly of polyester-type fibers and in which the fibers are bonded together locally and at a coarse density in such a manner that the former non-woven fabric serves as an intermediate layer and the latter non-woven fabrics serve as inner and outer layers, and subjecting the thus laminated material to the water-jet working, so that the fibers constituting the inner and outer layers are inserted in the melt-blown non-woven fabric and are intermingled with fibers in the melt-blown non-woven fabric or in the spun-bonded non-woven fabrics of the opposite sides, and that the layers are coupled together as a unitary structure.
In the present invention, the melt-blown non-woven fabric obtained by melt-blowing an olefin-type resin is used as an intermediate layer, i.e., as a core of the laminated non-woven fabric because of the reasons that it has the smallest weight among the fibers and it exhibits excellent softness, porosity, water resisting property and like properties. However, the melt-blown non-woven fabric has such problems that it is easily fluffed and lacks mechanical strength required for the non-woven fabric. In order to improve these problems according to the present invention, a spun-bonded non-woven fabric consisting chiefly of polyester fibers is laminated on both surfaces of the core to impart thereto excellent strength, hand, touch, etc. possessed by the spun-bonded non-woven fabric. According to the present invention, in this case, a distinguished feature resides in that use is made of a spun-bonded non-woven fabric or a pre-bonded non-woven fabric in which polyester-type fibers are bonded together locally and at a coarse density, and the laminated material is subjected to the water-jet working, so that the fibers of the spun-bonded non-woven fabric constituting the inner and outer layers are inserted in the melt-blown non-woven fabric and are intermingled with fibers in the melt-blown non-woven fabric or in the spun-bonded non-woven fabrics of the opposite sides, and that the layers are coupled together as a unitary structure.
The laminated non-woven fabrics comprising a melt-blown non-woven fabric of an olefin-type resin and a spun-bonded non-woven fabric of polyester-type fibers, have heretofore been known. However, these known laminated non-woven fabrics have all been stuck together by the heat-emboss working or the ultrasonic-wave working, causing the melt-adhered portions to be solidified and stiffened, and imparing softness, touch, hand and like properties as mentioned above.
There has further been known a water-jet method which uses a stream of water column of a high pressure and a high speed in order to mechanically intermingle the fibers in the non-woven fabric. It sounds very queer that the water-jet method was never employed for laminating the melt-blown non-woven fabric of the olefin-type resin and the spun-bonded non-woven fabric of the polyester-type fiber together. However, since fibers constituting the spun-bonded non-woven fabric were allowed to have a very small degree of freedom in the case of the above combination, it might have been difficult with the water-jet method to insert the fibers in the melt-blown non-woven fabric or to effectively intermingle the fibers with those of the spun-bonded non-woven fabric.
According to the present invention, on the other hand, it was discovered that when a spun-bonded non-woven fabric which consists chiefly of polyester-type fibers and in which fibers are bonded together locally and at a coarse density, is selected as a spun-bonded non-woven fabric of the polyester-type fibers and is combined with a melt-blown non-woven fabric of the olefin-type resin, the fibers of the spun-bonded non-woven fabric can be inserted in the melt-blown non-woven fabric when the laminated material is subjected to the water-jet working, and can hence be intermingled with fibers in the melt-blown non-woven fabric or with fibers in the spun-bonded non-woven fabrics of the opposite sides, enabling the non-woven fabrics to be coupled together as a unitary structure.
In the spun-bonded non-woven fabric of polyester-type fibers used in the present invention, it is particularly important that the fibers constituting the fabric are bonded together locally and at a coarse density. When the fibers are completely and strongly bonded together as in a conventional spun-bonded non-woven fabric, there is left no freedom for inserting the fibers in the melt-blown non-woven fabric or for the fibers to be intermingled with fibers in the melt-blown non-woven fabric or with fibers in the spun-bonded non-woven fabrics of the opposite side even when the laminated material is subjected to the water-jet working.
The laminated non-woven fabric of the present invention exhibits a strong interlayer anti-peeling property despite the intermediate layer of the melt-blown non-woven fabric and the inner and outer layers of a spun-bonded non-woven fabric are bonded together by a mechanical intermingling means, and further exhibits a markedly improved strength. Though the spun-bonded non-woven fabric used in the invention has a structure in which the fibers are bonded together locally and at a coarse density, the resulting laminated non-woven fabric exhibits a strong interlayer anti-peeling property and a markedly improved strength presumably due to that free fibers of the spun-bonded non-woven fabric are inserted in the melt-blown non-woven fabric and are intermingled with fibers in the melt-blown non-woven fabric or in the spun-bonded non-woven fabrics of the opposite sides, whereby fibers in the spun-bonded non-woven fabric lose freedom causing the non-woven fabrics to have an increased strength and further causing the non-woven fabrics to be firmly coupled together as a unitary structure. As a matter of course, the water-jet working advantageously brings about a function in that the filaments are little broken unlike that of the needlepunching.
The laminated non-woven fabric of the present invention does not have any melt-adhered portion between the melt-blown non-woven fabric and the spun-bonded non-woven fabrics; i.e., these non-woven fabrics are bonded together by a mechanical intermingling means, and features softness, touch and smoothness which are very superior to those obtained by the heat-embossing.